The present invention relates to a stable foam-forming system containing a blowing agent that is a gas at ambient temperature and pressure and to a process for the production of foams from this system.
Formulations and processes for the production of foams, particularly rigid polyurethane foams, are known. In recent years, foam producers have attempted to replace the ozone depleting CFC blowing agents with more environmentally desirable blowing agents. Among the blowing agents being evaluated and developed are hydrochloro-fluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). Many of these alternative blowing agents have sufficiently low boiling points that they are in the gaseous form at ambient temperature and pressure. Consequently, it has not been possible to incorporate these blowing agents into foam-forming formulations until very shortly before use without maintaining the formulation containing the blowing agent under temperature and pressure conditions that ensure the blowing agent stays in the liquid state. See, e.g., U.S. Pat. Nos. 3,541,023; 5,451,614; and 5,470,891.
In use, the gaseous blowing agent is typically added to the day tanks of the foam machine prior to foaming. The gaseous blowing agent may also be added to the "B-side" (i.e., the isocyanate-reactive component) during blending of that reaction component or it may be added as a separate, third stream from the mixhead. Blowing agent is generally included in the "B-side" of the foam-forming mixture in an amount of from about 3 to about 5% by weight.
The need to store a formulation into which blowing agent has been incorporated under controlled temperature and pressure conditions, however, increases the expense of handling and storing such formulation. It would therefore be advantageous to develop a foam-forming formulation into which a blowing agent that is a gas at ambient conditions could be incorporated and could subsequently be stored for some period of time at ambient temperature and pressure.
U.S. Pat. No. 4,972,003 teaches that use of an isocyanate-reactive compound having an equivalent weight of greater than 140 promotes the solubility of HCFC and HFC blowing agents having boiling points below 272.degree. K. This patent does not, however, teach that the disclosed mixtures of isocyanate-reactive compound and blowing agent are sufficiently stable that the blowing agent will remain in solution for an extended period of time. Nor does this disclosure suggest that foams can be produced from the disclosed "stable" composition by hand mixing.
It has now been found that unexpectedly high levels of a gaseous blowing agent may be incorporated into the B-side of a foam-forming composition at atmospheric pressure if a solubility-enhancing additive is included in the B-side. Blowing agents which may be successfully incorporated into the B-side include: monochloro-difluoro-methane (HCFC-22), 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124), 1,1,2,2-tetrafluoroethane (HFC-134), and 1,1,1,2-tetrafluoroethane (HFC-134a). These incorporated blowing agents do not separate from the other components present in the B-side and may be stored at ambient conditions in closed containers.